1. Field of the Invention
The present invention relates to a vehicle seat which comprises a seat back including a pad and a seat back frame supporting the pad, and a headrest provided on a top of the seat back.
2. Description of the Related Art
In a vehicle, particularly an automobile, with a view to measures against neck damage (whiplash injury) to an occupant (seated person) in the event of a rear collision, a headrest 41 is provided on a top of a seat back 40 of a vehicle seat, as shown in FIG. 12A. However, simply providing the headrest 41 is not enough for the whiplash injury measures.
Therefore, it has been proposed to couple a seat back frame and a cushioning S-spring (spring curved in a sinuous configuration) through a coupling member adapted to be stretched rearwardly only when a load having a given value or more is applied thereto (see JP 7-291005A).
In a vehicle seat disclosed in the above patent document, as shown in FIG. 12B, when a load from an occupant M is applied to the S-spring due to the reaction of a rear collision, the coupling member is stretched rearwardly, so that a back of the occupant M is deeply sunk into the seat back 40 to allow a head of the occupant is stopped by the head rest 41.
FIG. 12C shows a horizontal cross-section of the seat back 40. As shown in FIG. 12, the seat back 40 comprises a pad 43, and a base frame 42 supporting the pad 43. The base frame 42 has a pair of side frame sections 42a extending along respective ones of opposite lateral portions of the seat back 40. In a normal state, a front end 42b of each of the side frame sections 42a supports a rear surface of the pad 43 which receives a rearward load from the back of the occupant M. In FIG. 12C, the reference numeral 44 indicates a skin (trim) covering an outer surface of the pad 43.
In the event of a rear collision with a vehicle, due to the reaction of the rear collision, a large rearward load from the back of the occupant M is applied to the pad 43. Then, the pad 43 is pressed and flattened, and the back of the occupant M is displaced in such a manner as to be sunk into the seat back 40. In FIG. 12C, a contour of the back of the occupant M in the normal state is indicated by the line M-1, and a contour of the back of the occupant M during the rear collusion is indicated by the line M-2.
As above, during a rear collision with a vehicle, the back of the occupant M is urged to be displaced rearwardly while pressing and flattening the pad 43. However, actually, the rear surface of the pad 43 comes into contact with the front ends 42b of the right and left side frame sections 42a, so that deformation (flexural deformation in the rearward direction) of the pad 43 is hindered by the front ends 42b of the side frame sections 42a, and thereby a distance of the rearward displacement of the occupant M is restricted. Consequently, the line M-2 of the back of the occupant M during the rear collision is likely to become unable to be sufficiently displaced rearwardly, which leads to a risk of failing to adequate stop the head of the occupant by the head rest 41.